1. Field of the Invention
The present invention relates to a method for metallizing a surface and/or depositing metallic dots on a substrate, and particularly to a method. for metallizing a surface and/or depositing metallic dots on a substrate in which the surface can be electrically conductive or nonconductive.
2. Related Prior Art
Metallizing surfaces of substrates and/or depositing metallic dots on some substrates are significant in many industries and scientific technology, particularly in the manufacturing of printed circuit boards (PCBs), integrated circuits (ICs), Random Access Memory (RAM), chemical sensors, magnetic records and catalysts. In order to obtain plated films or dots with good adhesion as well as fine and tiny patterns on the nonconductive or semiconductive surfaces, proper pre-treatments before chemical plating (or electroless plating) are required. Especially, the metallic dots and/or dot arrays are difficult to be deposited or formed on a substrate without using photo-resisting pattern which is created by photolithography or other high-tech ways.
Patents including DE 38 06 884 C1, DE 39 23 832 A1, DE 39 31 003 A1, EP 02 06 133 A1 and EP 04 13 109 A2 mentioned some methods for forming a thin film of conductive polymers on the surfaces. However, the polymers may also deposited on the metal originally existing on the surface, which will results in poor adhesion between the metal plating later and the originally existing electrical contacts.
Patents including DE 39 39 676 C1, DE 41 12 462 A1, DE 42 27 836 A1 and GB 22 43 833 A provide solutions for the above problem, in which oxidants or acids are preliminarily added and adsorbed on the nonconductive surfaces. Unfortunately, applying such methods to semiconductor or ceramic substrates still does not produce with certainty the desired results. Moreover, the oxidants and acids are usually harmful to humans and so the health and safety of operators in the manufacturing process are put at risk.
U.S. Pat. Nos. 4,631,117, and 4,874,477 provide another solution by using conductive carbon black. However, the carbon black may be suitable for plated-through-hole technology (PTH) of PCBs, but not for the substrates with nonconducting surfaces and large areas.
U.S. Pat. Nos. 3,099,608, 3,099,608, 4,790,913 and No. 4,891,069 mentioned a pre-treatment procedure of activation in which Sn/Pd colloid solutions are added. A common disadvantage of using this method is that the operation conditions are strictly limited and thus the method cannot easily be applied to industries.
In U.S. Pat. Nos. 3,984,290, 4,895,739 4,952,286 5,007,990 5,017,742 and 4,810,333, depositing metal with higher reduction potential than copper, for example, the platinum group, on the substrates and etching are used. However, the operation conditions are also strictly limited.
However, all of the methods aforementioned are very complex and expensive, particularly due to the use of precious metals. Therefore, it is desirable to provide an improved method for metallizing surfaces of the substrates to mitigate and/or obviate the aforementioned problems.
The present invention iprovides a method for metallizing a surface and/or depositing metallic dots on a substrate, which can be completed by simple procedures.
The present invention also provides a method for metallizing a surface of a substrate, which can be completed without using precious metals and carcinogenic materials.
In The method of the present invention primarily includes steps of: a) pre-treating the surface of the substrate; b) positioning the substrate in an electroless plating reactor in which a heat source and an electrolyte are set at different temperatures, the substrate and the heat source forming a gap of 0.1 to 1000 xcexcm; and c) plating the substrate for a presetting duration.
The electrolyte may contain ions of Fe, Co, Ni, Cu, Ag, Au, Sn, Pt, Pd, etc., and particularly Ni2+ or Cu2+. The electrolyte is usually controlled at pH 3-13, and preferably at pH 4-9 or pH 12-13.
The substrate can be pre-treated by one or more procedures, for example, swelling, degreasing, coarsening, activation and washing.
The substrate and the heat source are usually separated at a gap of 0.1-1,000 xcexcm, and preferably 30-500 xcexcm. The substrate is preferably above the heat source.
The heat source is usually controlled at 50-200xc2x0 C., and preferably at 70-150xc2x0 C. The electrolyte is usually controlled at 10-80xc2x0 C., and preferably at 10-50xc2x0 C. In general, the heat source and the electrolyte can have a temperature difference ranging from 20xc2x0 C. to 120xc2x0 C., and preferably from 40xc2x0 C. to 100xc2x0 C.
The presetting duration for metallizing the substrate is usually between 10 seconds and 120 minutes, and preferably 1 minute to 90 minutes. The duration for depositing metallic dots or dot array is usually 10-1000 seconds, and preferably 30-800 seconds.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawing.